22106 research outputs found
Sort by
Effect of heterogeneity on confined liquid crystals under alternating electric fields
No full textThis study investigated the dynamics of the director rotation of liquid crystals (LCs) in a confined system in the presence of an alternating electric field. When the frequency of the electric field exceeded a critical value, LCs exhibited a phase delay in their response. LCs confined within smaller regions exhibited a higher critical frequency. Following the examination of the time scales of the electric field and director relaxation, the scaling of the critical frequency was numerically and theoretically investigated. The coupling between the increase in the threshold voltage and waveform changes the scaling of the critical frequency. © 2025 Taylor & Francis Group, LLC.journal articl
Perovskite solar cell modules: Understanding the device degradation via damp heat testing
No full textThe stability of flexible perovskite solar cell (PSC) modules based on methylammonium lead iodide (CH3NH3PbI3 or MAPbI3) was studied under damp heat (DH) stress test using barrier films with different level of water vapor transmission rates (WVTR) in the range of 5.0 × 10−3 and 7.4 × 10−1 g/m2/day measured at 85 °C. For this purpose, PSC modules were subjected to 2000 h DH-test (85 °C, 85 % relative humidity, RH). The photovoltaic (PV) performance of the modules showed different rates of degradation, which increased with increasing the WVTR value. For higher WVTR values, I-V curves depicted the 2nd diode component. Analysis of surface reflectance spectra and electroluminescence data confirmed the acceleration of degradation with increased WVTR value, which was expected to chemical decomposition of perovskite, and segregation of PbI2 at the interface acting as a hole-blocking layer. At 1000 h (2000 h) DH-test, the sample with lowest WVTR retained its 91.5 % (84.2 %) power conversion efficiency, i.e., mainly resulting from short-circuit current loss of −8% (−10 %). It has been shown that there is a threshold WVTR value to suppress the water vapor integration. Ultimately, this study highlights the importance of barrier film quality towards maintaining the long-term stability of PSC modules. © 2024 The Author(s)journal articl